var dataValidations = worksheet.DataValidations;
worksheet.Clear();
// dataValidations variable is no longer associated with worksheet, you need to do following to reacquire it
dataValidations = worksheet.DataValidations;

Dim dataValidations = worksheet.DataValidations
worksheet.Clear()
' dataValidations variable is no longer associated with worksheet, you need to do following to reacquire it
dataValidations = worksheet.DataValidations